1. Field of the Invention
The present invention relates to transferring context during hand-over of a mobile node in a wireless mesh network, and more particularly, the present invention relates to a system and method to perform incremental proactive context transfer according to analyzed wireless traffic characteristics in the wireless mesh network to minimize service delay in the moving mobile node while minimizing the consumption of Access Point (AP) resources.
2. Description of the Related Art
Up to the present, most typical Internet access has been enabled via wired networks such as Ethernet and Asymmetric Digital Subscriber Line (ADSL). The development of wireless communication technologies enables Internet access services based upon wireless connections rather than wired connections. Advanced approaches are also in the course of development to increase a transfer rate to that of wired networks.
Such wireless communication technologies are recently under active research, and include Wireless LAN (WLAN), mobile IP, MANET and so on. A representative example is Internet access via IEEE 802.11 wireless LAN technology. The WLAN technology being studied is focused on mobility-supporting technologies in which a user connected to the Internet via a WLAN is constantly provided with Internet access during movement regardless of the user's initial position.
The WLAN advantageously supports a specific service level, but there is a drawback in that it can only be used in a limited area. That is, a mobile node can be serviced only within a service available area of an AP but cannot be serviced out of the service available area of the AP. The mobile node cannot be provided with continuous service when it moves or roams to another AP.
Lately emerging is a wireless mesh network, that is, the so-called Metro Wireless LAN that is an owned network architecture for providing very high speed wireless access to a specific area. This technology can provide a coverage at least twice of that of conventional WLANs up to a radius of 1 to 2 km while supporting data communication such as Voice over Wireless LAN (VoWLAN). This technology is gaining attention as a solution which overwhelms existing hot spots.
The wireless mesh network is newly reinforced to enlarge WLAN technical support coverage, and is adapted to provide LAN-to-LAN connection wirelessly at an existing WLAN IEEE 802.11 frequency (2.4 GHz/5 GHz). That is, the wireless mesh network is mainly used to connect networks, whereas conventional LANs are used to support a number of users for connection.
In particular, while a conventional WLAN requires a wired connection at every AP, the wireless mesh network can enable wireless communication between APs so that a single wired connection together with WLANs can cover a wide area. Advantageously, this can be used in those areas in which Ethernet cables are not installed or in which installation thereof is difficult. However, a number of problems must be solved. For example, standardization for the wireless mesh network has not yet occurred, and market evidence is required for stability, compatibility and reliability. In addition, network installation is still restricted by legal limitations to WLAN power, interface problems related to the Industrial Scientific and Medical (ISM) band and fixed frequency requirements for networks.
In spite of these problems to be solved, the IEEE 802.11 wireless mesh network is increasing in use owing to its low installation cost and high bandwidth support compared to conventional Digital Subscriber Lines (DSLs) or cable-based networks.
The wireless mesh network serves to support the mobility of nodes, and has to transfer a service context such as physical layer connectivity, state, Quality of Service (QoS) and Authentication, Authorization and Accounting (AAA) when a node moves from one AP to another.
An inter AP hand-over of a mobile node in an IEEE 802.11 wireless mesh network is referred to as Inter Access Point (AP) Hand-over that a node is connected from one AP to another AP. When a node is moved from one AP to another AP, it is referred to as an Inter Access Point (AP) Hand-over. This process is called re-association according to IEEE 802.11 standards, and a context transfer in this process is called an L2 context transfer. When a node moves between APs which are connected to different access routers, it is referred to as an Inter Access Router Hand-over.
The hand-over process generally includes a detection step for detecting whether or not to change the AP to which a node is connected to a new AP, a search step for searching or probing for the new AP and an execution step for executing authentication and re-association.
The detection step determines whether a node will maintain its present connection with an original AP or move to a new AP through the data exchange with the original AP.
In the search step, the node transfers a probe signal to at least one surrounding AP to find a new AP, and upon receiving the probing signal, the at least one surrounding AP replies to the probe signal.
In the execution step, when the node requests authentication for the purpose of new connection with a new AP, the new AP sends an authentication result in response to the authentication request by the node, and the node is connected to the new AP.
According to system types, the execution step may proceed with transferring an Inter Access Point Protocol (IAPP) context. The IAPP context transfer is performed as follows: The new AP detects the IP address of the original AP from the MAC address provided by the node, and requests the original AP to reply with information necessary for the authentication of the node. At the request of the new AP, the original AP sends the information necessary for the authentication of the node to the new AP. Then, the new AP announces the connection of the node to surrounding APs, which in turn reply to the announcement.
When the authentication to the node has been successfully completed, the node requests the new AP for re-association, and the new AP responds to the re-association request by the node and proceeds with authentication for a higher protocol.
In the transfer of the IAPP context as discussed above, the new AP to which the node is newly connected via the IAPP MOVE procedure is provided with context information necessary for re-association and authentication from the original AP. Unfortunately, such a reactive context transfer induces a service delay when a mobile node is being provided with realtime multimedia service.
At present, a LAN card supporting IEEE 802.11x has not been enabled to support a soft hand-over unlike cellular communication. If a mobile node is provided with a realtime multimedia service, such as Voice over Internet Protocol (VoIP) and video streaming, existing reactive context transfer approaches can hardly support such a service that requires a delay time of 100 ms since they have a service delay time of 1 second or more.